Decoupled Water Reduction and Polyethylene Terephthalate Oxidation with KTi₂(PO₄)₃Redox Mediator for Solar Hydrogen Production

Water electrolysis powered by renewable energy represents a viable strategy for sustainable hydrogen production. However, the simultaneous occurrence of cathodic and anodic reactions faces challenges in terms of product separation and safety. Herein, a decoupled electrolysis system is constructed for separate solar H₂ generation and polyethylene terephthalate (PET) oxidation. Specifically, a KTi₂(PO₄)₃ (KTP) electrode is initially introduced as a mediator electrode for decoupled water electrolysis. Because the redox potential of KTP is close to the onset potential of the hydrogen evolution reaction (HER), the proposed decoupled water electrolyzer requires only 0.28 V to drive the H₂ production process at 5 mA. Such a voltage is conducive to using a solar cell to initiate hydrogen production. Further, the anodic oxygen evolution reaction (OER) is substituted by the oxidation of PET, realizing a membrane-free decoupled electrolyzer toward separate hydrogen production and PET oxidation. It is demonstrated that one Si solar cell can drive two decoupled HER cells in series for H₂ production in the daytime, and PET can be oxidized to produce formate at night. This work provides more flexibility to develop efficient electrolysis systems for energy and environmental applications.